SARS‐CoV‐2 has emerged as a human pathogen, causing clinical signs, from fever to pneumonia—COVID‐19—but may remain mild or asymptomatic. To understand the continuing spread of the virus, to detect ...those who are and were infected, and to follow the immune response longitudinally, reliable and robust assays for SARS‐CoV‐2 detection and immunological monitoring are needed. We quantified IgM, IgG, and IgA antibodies recognizing the SARS‐CoV‐2 receptor‐binding domain (RBD) or the Spike (S) protein over a period of 6 months following COVID‐19 onset. We report the detailed setup to monitor the humoral immune response from over 300 COVID‐19 hospital patients and healthcare workers, 2500 University staff, and 198 post‐COVID‐19 volunteers. Anti‐SARS‐CoV‐2 antibody responses follow a classic pattern with a rapid increase within the first three weeks after symptoms. Although titres reduce subsequently, the ability to detect anti‐SARS‐CoV‐2 IgG antibodies remained robust with confirmed neutralization activity for up to 6 months in a large proportion of previously virus‐positive screened subjects. Our work provides detailed information for the assays used, facilitating further and longitudinal analysis of protective immunity to SARS‐CoV‐2. Importantly, it highlights a continued level of circulating neutralising antibodies in most people with confirmed SARS‐CoV‐2.
The setup of a versatile COVID19 serology ELISA system is described, allowing Yes/No screening with a two‐step method that reduces false‐positives. Accurate antibody titer screening indicates a classic pattern of antibody production, peaking at 3 weeks post‐infection and remaining detectable for at least 6 months in 90% of the subjects tested. The antibody response does not correlate with age, but with severity of disease, and show an initial higher response in men.
In the last few decades, considerable efforts have been made toward the development of efficient vaccines against malaria. Whole‐sporozoite (Wsp) vaccines, which induce efficient immune responses ...against the pre‐erythrocytic (PE) stages (sporozoites and liver forms) of Plasmodium parasites, the causative agents of malaria, are among the most promising immunization strategies tested until present. Several Wsp PE vaccination approaches are currently under evaluation in the clinic, including radiation‐ or genetically‐attenuated Plasmodium sporozoites, live parasites combined with chemoprophylaxis, or genetically modified rodent Plasmodium parasites. In addition to the assessment of their protective efficacy, clinical trials of Wsp PE vaccine candidates inevitably involve the thorough investigation of the immune responses elicited by vaccination, as well as the identification of correlates of protection. Here, we review the main methodologies employed to dissect the humoral and cellular immune responses observed in the context of Wsp PE vaccine clinical trials and discuss future strategies to further deepen the knowledge generated by these studies, providing a toolbox for the in‐depth analysis of vaccine‐induced immunogenicity.
Whole‐sporozoite (Wsp) vaccines, employing attenuated malaria parasites, are among the most promising candidates for vaccination against this devastating disease. The evaluation of Wsp vaccines in human volunteers is essential not only to assess their protective efficacy, but also to investigate the immunity elicited by vaccination and identify correlates of protection. We review current and future methodologies to evaluate the immune responses triggered by Wsp vaccines in the clinic.
The transmissible forms of Plasmodium parasites result from a process of sporogony that takes place inside their obligatory mosquito vector and culminates in the formation of mammalian-infective ...parasite forms. Ivermectin is a member of the avermectin family of endectocides, which has been proposed to inhibit malaria transmission due its insecticidal effect. However, it remains unclear whether ivermectin also exerts a direct action on the parasite's blood and transmission stages.
We employed a rodent model of infection to assess the impact of ivermectin treatment on P. berghei asexual and sexual blood forms in vivo. We then made use of a newly established luminescence-based methodology to evaluate the activity of ivermectin and other avermectins against the sporogonic stages of P. berghei parasites in vitro independent of their role on mosquito physiology.
Our results show that whereas ivermectin does not affect the parasite's parasitemia, gametocytemia or exflagellation in the mammalian host, several members of the avermectin family of compounds exert a strong inhibitory effect on the generation and development of P. berghei oocysts.
Our results shed light on the action of avermectins against Plasmodium transmission stages and highlight the potential of these compounds to help prevent the spread of malaria.
Long-term protection against malaria remains one of the greatest challenges of vaccination against this deadly parasitic disease. Whole-sporozoite (WSp) malaria vaccine formulations, which target the ...Plasmodium parasite’s pre-erythrocytic stages, include radiation-attenuated sporozoites (RAS), early- and late-arresting genetically-attenuated parasites (EA-GAP and LA-GAP, respectively), and chemoprophylaxis with sporozoites (CPS). Although all these four vaccine formulations induce protective immune responses in the clinic, data on the longevity of the antimalarial protection they afford remain scarce. We employed a mouse model of malaria to assess protection conferred by immunization with P. berghei (Pb)-based surrogates of these four WSp formulations over a 36-week period. We show that EA-GAP WSp provide the lowest overall protection against an infectious Pb challenge, and that while immunization with RAS and LA-GAP WSp elicits the most durable protection, the protective efficacy of CPS WSp wanes rapidly over the 36-week period, most notably at higher immunization dosages. Analyses of liver immune cells show that CD44hi CD8+ T cells in CPS WSp-immunized mice express increased levels of the co-inhibitory PD-1 and LAG-3 markers compared to mice immunized with the other WSp formulations. This indicates that memory CD8+ T cells elicited by CPS WSp immunization display a more exhausted phenotype, which may explain the rapid waning of protection conferred by the former. These results emphasize the need for a detailed comparison of the duration of protection of different WSp formulations in humans and suggest a more beneficial effect of RAS and LA-GAP WSp compared to EA-GAP or CSP WSp.
Coendemicity between the human immunodeficiency virus (HIV) and
parasites, the causative agents of acquired immunodeficiency syndrome (AIDS) and malaria, respectively, occurs in several regions ...around the world. Although the impact of the interaction between these two organisms is not well understood, it is thought that the outcome of either disease may be negatively influenced by coinfection. Therefore, it is important to understand how current first-line antiretroviral therapies (ART) might impact
infection in these regions. Here, we describe the effect of 18 antiretroviral compounds and of first-line ART on the blood and sporogonic stages of
and
. We show that the combination zidovudine + lamivudine + lopinavir/ritonavir (LPV/r), employed as first-line HIV treatment in the field, has a strong inhibitory activity on the sporogonic stages of
and that several non-nucleoside reverse transcriptase inhibitors (NNRTI) have a moderate effect on this stage of the parasite's life cycle. Our results expose the effect of current first-line ART on
infection and identify potential alternative therapies for HIV/AIDS that might impact malaria transmission.
Avermectins are powerful endectocides with an established potential to reduce the incidence of vector-borne diseases. Here, we show that several avermectins inhibit the hepatic stage of Plasmodium ...infection in vitro Notably, ivermectin potently inhibits liver infection in vivo by impairing parasite development inside hepatocytes. This impairment has a clear impact on the ensuing blood stage parasitemia, reducing disease severity and enhancing host survival. Ivermectin has been proposed as a tool to control malaria transmission because of its effects on the mosquito vector. Our study extends the effect of ivermectin to the early stages of mammalian host infection and supports the inclusion of this multipurpose drug in malaria control strategies.
Sleeping sickness and malaria are parasitic diseases with overlapping geographical distributions in sub-Saharan Africa. We hypothesized that the immune response elicited by an infection with ...Trypanosoma brucei, the etiological agent of sleeping sickness, would inhibit a subsequent infection by Plasmodium, the malaria parasite, decreasing the severity of its associated pathology. To investigate this, we established a new co-infection model in which mice were initially infected with T. brucei, followed by administration of P. berghei sporozoites. We observed that a primary infection by T. brucei significantly attenuates a subsequent infection by the malaria parasite, protecting mice from experimental cerebral malaria and prolonging host survival. We further observed that an ongoing T. brucei infection leads to an accumulation of lymphocyte-derived IFN-γ in the liver, limiting the establishment of a subsequent hepatic infection by P. berghei sporozoites. Thus, we identified a novel host-mediated interaction between two parasitic infections, which may be epidemiologically relevant in regions of Trypanosoma/Plasmodium co-endemicity.
•Agent-based model of malaria spreading, validated with empirical data for the transmission aspects of this phenomenon.•Uncover of a phase transition from prevalence to eradication, by small ...variations of drug therapies actions.•Derivation of critical values of the parameters characterizing the effect of each drug therapy.•Emphasis on gametocytemia reduction and on the selective mosquito mortality during parasite development in the mosquito.•Quantitative evidence of what is empirically known concerning combined therapies.
We introduce an agent-based model describing a susceptible-infectious-susceptible (SIS) system of humans and mosquitoes to predict malaria epidemiological scenarios in realistic biological conditions. Emphasis is given to the transition from endemic behavior to eradication of malaria transmission induced by combined drug therapies acting on both the gametocytemia reduction and on the selective mosquito mortality during parasite development in the mosquito. Our mathematical framework enables to uncover the critical values of the parameters characterizing the effect of each drug therapy. Moreover, our results provide quantitative evidence of what was up to now only partially assumed with empirical support: interventions combining gametocytemia reduction through the use of gametocidal drugs, with the selective action of ivermectin during parasite development in the mosquito, may actively promote disease eradication in the long run. In the agent model, the main properties of human-mosquito interactions are implemented as parameters and the model is validated by comparing simulations with real data of malaria incidence collected in the endemic malaria region of Chimoio in Mozambique. Finally, we discuss our findings in light of current drug administration strategies for malaria prevention, which may interfere with human-to-mosquito transmission process.
Prior to infecting erythrocytes and causing malaria symptoms, Plasmodium parasites undergo an obligatory phase of invasion and extensive replication inside their mammalian host's liver cells that ...depends on the parasite's ability to obtain the nutrients it requires for its intra-hepatic growth and multiplication. Here, we show that L-arginine (Arg) uptake through the host cell's SLC7A2-encoded transporters is essential for the parasite's development and maturation in the liver. Our data suggest that the Arg that is taken up is primarily metabolized by the arginase pathway to produce the polyamines required for Plasmodium growth. Although the parasite may hijack the host's biosynthesis pathway, it relies mainly upon its own arginase-AdoMetDC/ODC pathway to acquire the polyamines it needs to develop. These results identify for the first time a pivotal role for Arg-dependent polyamine production during Plasmodium's hepatic development and pave the way to the exploitation of strategies to impact liver infection by the malaria parasite through the modulation of Arg uptake and polyamine synthesis.
Malaria remains one of the world's most prevalent infectious diseases. Several vaccination strategies currently under investigation aim at hampering the development of the
parasite during the ...clinically silent liver stage of its life cycle in the mammalian host, preventing the subsequent disease-associated blood stage of infection. Immunization with radiation-attenuated sporozoites (RAS), the liver-infecting parasite forms, can induce sterile protection against malaria. However, the efficacy of vaccine candidates in malaria-naïve individuals in high-income countries is frequently higher than that found in populations where malaria is endemic. Malnutrition has been associated with immune dysfunction and with a delay or impairment of the immune response to some vaccines. Since vaccine efficacy depends on the generation of competent immune responses, and malaria-endemic regions are often associated with malnutrition, we hypothesized that an inadequate host nutritional status, specifically resulting from a reduction in dietary protein, could impact on the establishment of an efficient anti-malarial immune response. We developed a model of RAS immunization under low protein diet to investigate the impact of a reduced host protein intake on the immunogenicity and protective efficacy of this vaccine. Our analysis of the circulating and tissue-associated immune compartments revealed that a reduction in dietary protein intake during immunization resulted in a decrease in the frequency of circulating CD4+ T cells and of hepatic NK cells. Nevertheless, the profile of CD8+ T cells in the blood, liver and spleen was robust and minimally affected by the dietary protein content during RAS immunization, as assessed by supervised and in-depth unsupervised X-shift clustering analysis. Although mice immunized under low protein diet presented higher parasite liver load upon challenge than those immunized under adequate protein intake, the two groups displayed similar levels of protection from disease. Overall, our data indicate that dietary protein reduction may have minimal impact on the immunogenicity and efficacy of RAS-based malaria vaccination. Importantly, this experimental model can be extended to assess the impact of other nutrient imbalances and immunization strategies, towards the refinement of future translational interventions that improve vaccine efficacy in malnourished individuals.
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